Two-pass method and apparatus for achieving maximal data compression for a modem relay mode of operation in a voice frame network

ABSTRACT

The present invention is a two-pass method and apparatus for achieving maximal data compression for a voice frame modem relay channel between two endpoint modems. The method includes transitioning the channel from a voice mode to a modem relay mode of operation; negotiating maximal compression parameters for either of two endpoint segments; communicating the same from one segment to the other; and then negotiating maximal end-to-end data compression parameters based upon the negotiated endpoint segment compression parameters. The end-to-end negotiation preferably involves re-negotiating one of the endpoint segments. The apparatus includes a dual first-pass negotiation mechanism for independently determining the maximal data compression capability of each segment; an end-to-end data compression capability determination mechanism for determining the maximal end-to-end data compression capability based upon the independently determined capability of each segment; and a second-pass negotiation mechanism for establishing the determined maximal end-to-end data compression capability for the channel.

RELATED APPLICATIONS

[0001] This application is a continuation-in-part of co-pending U.S.patent application Ser. No. 09/______, filed Nov. 16, 2000 entitledHIGH-SPEED DIAL-UP MODEM SESSION STARTUP METHOD AND APPARATUS, subjectto common ownership herewith by Cisco Technology, Inc.

BACKGROUND OF THE INVENTION

[0002] The present invention relates generally to voice frame networksystems such as Voice over Internet Protocol (VoIP) systems forconcurrently carrying both voice and data signals, and more particularlyit concerns method and apparatus for transitioning a high-speed datachannel from voice mode to modem relay mode during session startup.

[0003] VoIP is widely deployed by Internet Service Providers (ISPs) andwithin large or distributed private enterprises. Because voice channelsrequire low latency for audio continuity and understanding in humanconversation, typical VoIP implementations have utilized low-latencymechanisms such as Real-time Transfer Protocol (RTP). Unfortunately, thevoice mode of VoIP channels that use RTP is an unreliable transportmechanism for high-speed modem signals. High packet drop rates andfrequent retrains cause undesirable deterioration of the signal whenhigh-speed modem signals are carried over a standard VoIP channel.

SUMMARY OF THE INVENTION

[0004] The present invention is a two-pass method and apparatus forachieving maximal data compression for a voice frame modem relay channelbetween two endpoint modems. The method includes transitioning thechannel from a voice mode to a modem relay mode of operation;negotiating maximal compression parameters for either of two endpointsegments; communicating the same from one segment to the other; and thennegotiating maximal end-to-end data compression parameters based uponthe negotiated endpoint segment compression parameters. The end-to-endnegotiation preferably involves re-negotiating one of the endpointsegments. The apparatus includes a dual first-pass negotiation mechanismfor independently determining the maximal data compression capability ofeach segment; an end-to-end data compression capability determinationmechanism for determining the maximal end-to-end data compressioncapability based upon the independently determined capability of eachsegment; and a second-pass negotiation mechanism for establishing thedetermined maximal end-to-end data compression capability for thechannel.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005]FIG. 1 is a system block diagram illustrating a VoIP network inwhich the two-pass capability-exchange apparatus is featured inaccordance with a preferred embodiment of the invention.

[0006]FIG. 2 is a flowchart of the voice mode-to-modem relay modetransition method in accordance with a preferred embodiment of theinvention.

[0007]FIG. 3 is a flowchart of the maximal compression method inaccordance with a preferred embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0008]FIG. 1 illustrates the invented apparatus 8 coupled with a network10 operating with respect to voice traffic thereon in accordance with avoice packet protocol such as a voice over frame relay (VoFR) protocolor voice over Internet protocol (VoIp). Network 10 typically includesone or more telephone handsets 12, one or more fax machines 14 and oneor more low-speed modems 16 representing different traffic demands onnetwork 10 due to their diverse bandwidth requirements. The faxes 14 andlow-speed modems 16 often share telephone numbers with the telephonehandsets to provide facsimile, e-mail and Internet service tousers/clients. High-speed modems 16′ having data rates of 32 k-56kbits/second (kbps) or higher are typically provided, and are the typeof high-speed modems with which the invention finds particular utility.

[0009] Handsets 12 communicating voice typically require bit rates ofapproximately 8 k-64 kbps over the IP network. Typically, pluralhandsets 12 are connected with each one of plural voice gateways 18representing so-called endpoint nodes within network 10. Handsets 12will be understood to be used for voice communication, whereby voicesignals are digitized, packetized and transmitted bi-directionallyduring a telephone conversation. In a voice frame network like network10, concurrent with voice traffic over the network is the presence of anincreasing volume of data traffic.

[0010] Those of skill in the art will appreciate that data and voicetraffic are compatible to some extent because both are represented innetwork 10 in digital form. But voice and data traffic have differentrequirements, especially under increasing traffic demands. For example,voice traffic requires low latency because of the need for immediatefeedback or other form of acknowledgement in a two-way humanconversation. In voice mode, VoIP channels using RTP or otherlow-latency protocols represent an unreliable transport for high-speedsignaling between high-speed modems 16′. Conventionally, in a VoIPnetwork 10, high-speed modems 16′ would have negotiated an end-to-endphysical layer, e.g. V.34, and gateways 18 would have been passiveenablers of the resulting voice mode VoIP connection which is subject tohigh packet drop rates and frequent retrains.

[0011] The invented solution to the problem described above is toterminate the physical layer, e.g. V.34, at the VoIP gateway, and topacketize and transmit the demodulated data bit stream over the IPnetwork to the peer gateway where it is reconstructed and forwarded tothe receiving modem. This is referred to as a modem relay mode ofoperation. By monitoring physical layer negotiation between theoriginating and answering endpoints during a predeterminedly early phaseof the end-to-end negotiation between endpoints, it is determinedwhether the endpoints are modems negotiating a high-speed dial-upconnection. If so, the VoIP gateways take over the end-to-endnegotiation of the physical layer, terminating the physical layerlocally on their adjacent telephony segment.

[0012] Modem relay startup must first determine that the originating andanswering modems are high-speed modems through appropriate tonedetection sensitive enough to distinguish low-speed modem 16 and fax 14signals from high-speed modem 16′ dial-up connections. It must thensmoothly transition to modem relay mode at an appropriate time and in anon-disruptive manner during the sensitive end-to-end physical layernegotiation. For example, consider an enterprise with a dial-up serveror machine S in a central office at location X and an employee at homewho tries to make a dial-up connection from the employee's clientend-station or machine C at location Y.

[0013] Assume the dial-up connection is made through a phone company Pthat provides the dial-up connection over a phone company P VoIPnetwork. Such a call would have three segments:

[0014] a) Segment 1: a telephony segment from client C to phone companyP (e.g. local loop on the client end). This will be referred to hereinas the calling leg.

[0015] b) Segment 2: a VoIP segment within phone company P.

[0016] c) Segment 3: a telephony segment from phone company P to serverS (e.g. local loop on the server end). This will be referred to hereinas the called leg.

[0017] Further assume that server machine S and client machine C areconnected to the dial-up circuit through a high-speed modem 16′ and thatinitially the VoIP channel is in voice mode.

[0018] Further assume that the physical layer (e.g., V.34) and the errorcorrection layer (e.g. V.42) are terminated locally on the VoIPgateways, but the de/compression layer (e.g. V.42bis) is not terminatedon the gateways and is performed end-to-end by the client modems. Thoseof skill in the art will appreciate that, for the above modem relayfunction to work, segments 1 and 3 must have the same compressionparameters. This includes the following three parameters for V.42bis:

[0019] 1) V.42bis PO:PV, which identifies in which direction compressionis performed,

[0020]2) V.42bis PI :Pv, which is the Number of V.42bis Codewords,

[0021]3) V.42bis P2:PV, which is V.42bis maximum String Length. However,the V.42bis parameters are negotiated independently on segment 1 andsegment 3. In segment 1 the negotiation occurs, between client C modemand its adjacent VoIP gateway from the phone company. In segment 3 thenegotiation occurs between server S modem and its adjacent VoIP gateway.

[0022] This means there are four negotiating parties:

[0023] 1,2) two VoIP gateways,

[0024] 3) the client C modem, and

[0025] 4) the server S modem; and two separate negotiation processes:

[0026] 1) between the client C modem and its VoIP gateway, and

[0027] 2) between the server S modem and its VoIP gateway.

[0028] As described above, for modem relay to work with V.42bisperformed on the modems (instead of gateways), the two negotiationprocesses listed above must produce the same outcome. However, themaximal compression capability of the client C modem, the server Smodem, and the VoIP gateways can be quite different. Moreover, if thetwo negotiation processes are conducted independently, there is noguarantee that the outcome will be the same.

[0029] A simple approach to achieve the same negotiated set ofcompression parameters on segment 1 and segment 3 is for the VoIPgateways to use a minimalist approach. For example, the VoIP gatewaysmay negotiate the smallest allowed values for “Number of Codewords”, and“Maximum String Length”. As long as the parameters used are so smallthat all modem makes or models from various manufacturers can supportthem, this would result in the same negotiated set, which is desirable.However, this also means the modem relay session would have a verysub-optimal compression characteristics. Much higher compression ratiosmay be achievable between the client C and server S modems, ifcompression is based on the actual capabilities of the two modems.

[0030] The present invention involves maximizing data compression basedupon the actual capability of the client C and server S modems. Muchhigher compression ratios thus are possible with the invention, comparedto the simplistic approach of using minimal compression parameters, the‘least common denominator’ approach described above.

[0031]FIG. 2 is a flowchart illustrating the high-speed modem relayconnection method in accordance with a preferred embodiment of theinvention. The invented high-speed dial-up modem session startup methodproceeds in five numbered steps as follows:

[0032] 1) A VoIP gateway on the called leg is conditioned to detect anITU-T V.8 amplitude-modulated answer tone (ANSam) signal on the streamat least from server machine S's modem to the VoIP gateway. Those ofskill in the art will appreciate that detecting the ANSam signal is astrong indication that the answering modem (e.g. the server machine Smodem in this example) supports high-speed dial-up connection via aV.34-compliant modem. The evolving ITU-T Recommendation V.8 (hereinafterthe V.8 standard) is described in a February 1998 publication of theInternational Telecommunication Union entitled Series V: DataCommunication Over The Telephone Network and subtitled Procedures ForStarting Sessions Of Data Transmission Over The Public SwitchedTelephone Network.

[0033] In accordance with the preferred embodiment of the invention,either gateway is conditioned to detect ANSam. Occasionally, ANSamechoes back from a call-originating modem to the call-answering modemthat generated the ANSam signal. Due to needed high-sensitivity in thetone detectors, ANSam then may be detected at either end. Because theearliest possible detection of ANSam is desired, in accordance with theinvention, the gateways of both the called leg and the calling leg areconditioned to detect ANSam. The first gateway to detect ANSam thensimply signals the other gateway that ANSam has been detected. Those ofskill in the art will appreciate that such signaling may be performed inany suitable manner, e.g. via known out-of-band gateway-to-gatewaysignaling techniques.

[0034] Step 1 including ANSam tone detection is illustrated in FIG. 2 at100 and 102.

[0035] 2) As soon as the ANSam signal is detected, the channel is placedin a passthrough state by disabling voice compression and echocancellation. This is accomplished preferably at both gateways, wherebythe ANSam signal-detecting gateway signals the other gateway and bothgateways proceed as follows. Voice compression is disabled (i.e. thechannel is required to switch over to uncompressed G7 11 mode), assumingcompression previously was enabled. (Those of skill in the art willappreciate this allows the least amount of distortion in the modemsignals on the channel.) Also, voice echo cancellation is disabled,assuming it previously was enabled in voice mode. (Those of skill willappreciate that during the modem physical layer training phase, themodems configure their own echo cancellation parameters, which are usedsubsequently by the modems for echo cancellation.)

[0036] Next, and as part of step 2, the VoIP gateway on the calling legis conditioned to detect a V.8 call menu (CM) signal (a digital codegenerated by a high-speed originating modem to indicate the fact) on thestream arriving from the originating modem on the calling leg. This is afurther indication that modem relay transition is desired because itindicates that the originating modem is a high-speed modem compliantwith V.34. (Those of skill in the art will appreciate that detection ofa V.8 CM signal is important in accordance with the preferred embodimentof the invention by brief consideration of the case where theoriginating modem is V.32 and the answering modem is V.34. In such case,ANSam would be generated on the called leg, but there would be no CMgeneration.)

[0037] Those of skill in the art will appreciate that, in accordancewith the preferred embodiment of the invention, both gateways areconditioned to detect CM even though it is the calling leg thatgenerates CM. It is within the spirit and scope of the invention,however, to condition only the called-leg gateway to detect CM, assumingthe called-leg gateway can be identified with sufficiently highprobability.

[0038] Step 2 including CM code detection is illustrated in FIG. 2 at200 and 202.

[0039] 3) Upon CM detection, the CM-detecting gateway silences orsuppresses transmission of modem signals to the other leg. This is toavoid undesirable end-to-end negotiation between the two modems thatwould otherwise result if successive identical CMs generated by thecaller modem were received by the answering modem (which under a typicalprotocol would respond with a V.8 joint menu (JM) signal or code). Thephenomenon whereby CM undesirably reaches the far end is referred toherein as CM leakage from the calling leg to the called leg. Inaccordance with the invention in its preferred embodiment, CM leakage isavoided.

[0040] Step 3 is illustrated in FIG. 2 at 300.

[0041] 4) After signal suppression, the VoIP gateways undertake physicallayer negotiation, effectively usurping the modems' normal role andpreventing the modems from completing end-to-end negotiation. Those ofskill in the art will appreciate that, by this time, the originating andanswering modems already are partway through V.34 Phase 1 negotiation,which was conducted end-to-end by the modems via exchange of ANSam andCM. In accordance with the invention, the V.34 stacks on the VoIPgateways accommodate for this fact as follows.

[0042] 4a) On the calling leg, the VoIP gateway acts like an answeringmodem in Phase 1 but begins with a local truncated V.34 Phase 1negotiation. Phase 1 negotiation is continued by the gateway at thepoint subsequent to generation of the ANSam signal (i.e. the gatewayneed not generate any additional ANSam tones). The gateway awaits twoadditional CMs from the originating modem (e.g. the client machine Cmodem, in this example). When two additional identical CMs are received,the calling-leg gateway proceeds with the rest of V.34 Phase 1 andsubsequent physical layer startup as usual (i.e. as specified in the V.8standard).

[0043] Step 4 a, including determining which leg gateway 18 is in, isillustrated in FIG. 2 at 400 and 400 a.

[0044]4 b) On the called leg, the VoIP gateway acts like an originatingmodem in Phase 1 but begins with a local truncated V.34 Phase 1negotiation. Phase 1 negotiation is continued by the gateway at thepoint subsequent to generation of CM since the answering modem (e.g. theserver machine S modem, in this example) already has generated ANSam.Thus, the called-leg gateway begins generating at least two identicalCMs immediately and proceeds with the rest of Phase 1 and subsequentphysical layer startup as usual (i.e. as specified in the V.8 standard).

[0045] Step 4 b is illustrated in FIG. 2 at 400 b.

[0046] 5) With the transition complete, local physical layer negotiationon Segment 1 (between client machine C modem and its associated VoIPgateway) and Segment 3 (between server machine S modem and itsassociated VoIP gateway) have supplanted the initial end-to-endnegotiation between the two modems. A modem relay session is establishedend to end in the form of a high-speed dial-up connection that is farmore reliable than traditional voice mode connections within VoIPnetworks.

[0047] Step 5 is illustrated in FIG. 2 at 500.

[0048] In accordance with a preferred embodiment of the invention, CMsignal tone detection in step 2) above may be performed as follows. TheVoIP gateway demodulates the bit stream and looks for a specific bitpattern identifying modem CM. In the case of aV.8 modem,thebitpatternis11111111110000001111 0100000111. The leading twenty bits represent theCM/JM wake-up and synchronize header. The trailing ten bits include aninformation octet (framed by start and stop bits) that represents thecall function and V-Series modem type. The modem type should be V.34 orhigher speed modem 16′, in accordance with the invention.

[0049]FIG. 3 illustrates the preferred method of the invention by whicha two-pass capability exchange between high-speed dial-up modemsachieves maximal compression based upon the maximum compressioncapability of both modems.

[0050] The approach presented here is described in terms of V.42biscompression parameters (and negotiation scheme). In other words, it isassumed that both the client C and the server S modems are V34NV.42bismodems. Those of skill in the art will appreciate, however, that, withinthe spirit and scope of the invention, other modems may be similarlyaccommodated. Thus, V34NV.42bis modems are described by way ofillustration only and not by way of limitation, as the two-passcapability exchange method has a more general applicability, and theinvented method is readily applicable to solve a wide set of negotiationproblems having similar characteristics.

[0051] In a preferred embodiment of the invention, the following stepsare realized.

[0052] 1) A first pass detects the maximal compression capability of theadjacent modem on the called leg;

[0053] 2) The maximal compression capability feasible end-to-end isdetermined (e.g. by determining the maximal compression capability ofthe adjacent modem on the calling leg, by communicating the called legdata compression capability to the calling leg and by establishingmaximal compression parameters based thereon at the calling leg); and

[0054] 3) A second pass renegotiates the called leg data compressionparameters based on the maximal capability that is feasible end-to-end.

[0055] Referring to FIG. 3, the invented method will now be described inmore detail.

[0056] Negotiation pass 1 determines the maximal capability of theadjacent modem on the called leg. The purpose of the first negotiationpass is to discover the maximal compression capability that can beachieved by the client C modem on the called leg. At the end of thisstep, for segment 3, the VoIP gateway determines the maximal capabilityof client C modem. To determine the maximal capability of the modem, theVoIP gateway assumes the following V.42bis compression parameters as itsnegotiation posture:

[0057] V.42bis P0:PV=11 (request compression in both directions),

[0058] V.42bis P1:PV=65535 (Number of Codewords),

[0059] V.42bis P2:PV=255 (Maximum String Length).

[0060] The above constitutes maximal values for P0, P1, and P2. Takingthis set as its negotiation posture (during V.42 XID exchange), the VoIPgateway is able to determine the maximum actual compression capabilityfeasible by the adjacent modem on segment 3.

[0061] The next step is to determine the maximal compression capabilitythat is feasible end-to-end. Once the maximum capability is known onsegment 3, the VoIP gateway on segment 3 must notify (e.g. signal orotherwise communicate to) the peer VoIP gateway on segment 1 of themaximal compression capability feasible on its segment. Those of skillin the art will appreciate that negotiation on segment 3 must becompleted without timing out on segment 1. Thus, subsequent totransition into modem relay state (as described above and in ourabove-referenced co-pending patent application or by other suitablemeans), the gateway on segment 1 declines (“refuses”) to respond back toV.8 CM generated by client modem on segment 1. It so declines to responduntil it has received notification of the negotiation result on segment3 from the VoIP gateway on segment 3. This means physical layer bring-upon segment 1 is delayed after transition into the modem relay state ormode of operation. While XID negotiation is performed at segment 3, thestatus of segment 1 involves the client C modem generating CMs, butreceiving silence in return from the VoIP gateway on segment 1.

[0062] Once the VoIP gateway on segment 1 is notified of XID negotiationresult on segment 3, it brings up its physical layer. The physical layeris brought up by responding to CM from the client C modem on segment 1with an appropriate V.8 JM and by performing the rest of physical layerbring-up in a conventional manner, e.g. in accordance with the ITU-T V.8protocol.

[0063] The VoIP gateway on segment 1 then uses the result of XIDnegotiation on segment 3 as its negotiation posture, and responds to XIDgenerated by client modem C on segment 1 (assuming V.42 operation onsegment 1), based on this negotiation posture XID negotiation on segment1 determines the maximal end-to-end V.42bis parameters that can beestablished between the two modems. The VoIP gateway on segment 1informs its peer VoIP gateway on segment 3 as to the result of the XIDnegotiation on segment 1, i.e. the segment1 gateway signals the segment3 gateway by any suitable signaling technique.

[0064] Negotiation pass 2 renegotiates on the called leg based upon themaximal capability that is feasible end-to-end. Once the end-to-endmaximal capability is known to the VoIP gateway on segment 3, itrenegotiates the data compression parameters on its segment. This isdone by releasing the telephony segment 3 and redialing (reestablishing)the telephone half leg on segment 3. This reinitializes the physicallayer and the V.42/V.42bis stacks on the VoIP gateway and client modemand allows the XID parameter negotiation to be repeated on segment 3.However, during this second-pass negotiation, the VoIP gateway onsegment 3 assumes the end-to-end negotiation parameters determined instep 2 as its negotiation posture. This results in the use ofcompression parameters that represent the maximal set achievable by thetwo modems, as desired.

[0065] The VoIP gateways maintain this end-to-end set of compressionparameters as their negotiation posture for the rest of the modem relaysession (in case of any other XID negotiations that may occur throughthe remaining lifetime of the modem relay session). They do so inaccordance with the invention by storing such parameters in memory. Thismeans if there are any subsequent attempts by client or server modems Cor S to change the established compression parameters during the datatransfer phase, these would have no effect on the established negotiatedset. (Such renegotiation is not allowed also by the V.42bisspecification, and should not be expected. Nevertheless, as a precautionsuch parameters are stored and maintained in accordance with theinvention).

[0066] Referring again now to FIG. 1, apparatus 8 will be described inmore detail. Apparatus 8, which may be thought of as including a modemrelay connection mechanism or modem relay connector, includes an ANSamtone detector 20; a passthrough (pass-thru) mode invocation mechanism22; and preferably also a remote-gateway (remote-GW) signaling mechanism24. Apparatus 8 also includes a CM code detector 26; a signalsuppression mechanism 28; and a local proxy negotiation mechanism 30. Aswill be understood from the above description of the invented method,ANSam detector 20 causes pass-through mode invocation mechanism 22 todisable voice compression and cancellation if either or both aredetermined to have been enabled. ANSam detector 20 also causes remote-GWsignaling mechanism 24 to signal the remote gateway 18 connected to thefar-end modem. Those of skill in the art will appreciate that it is notyet determined to a high degree of certainty that both modems arehigh-speed.

[0067] Upon detection of a CM code by code detector 26, the transitionto modem relay mode may begin, since detection of a CM code by eithergateway 18 indicates that a high-speed modem 16′ has received an ANSamfrom another high-speed modem 16′ in accordance with the V.34 protocol.Thus, CM code detector 26 causes a signal suppression mechanism 28immediately to suppress further signals between high-speed modems 16′,effectively terminating the end-to-end physical layer negotiationstherebetween. Once signals have been suppressed—at what is referred toherein as a predeterminedly early time in the end-to-endnegotiations—local proxy negotiation mechanism 30 transmits or detectsconsecutive identical CM codes, as described above, and then completeslocal physical layer negotiation in accordance with the high-speed,dial-up V.34 modem protocol.

[0068] Referring still to FIG. 1, apparatus 8 may be seen further toinclude a two-pass capability exchange mechanism or exchanger 32.Capability exchanger 32 includes a dual first-pass negotiation mechanism34, an end-to-end data compression capability determination mechanism36, and a second pass end-to-end re-negotiation mechanism 38.Preferably, exchanger 32 further includes an end-to-end negotiationposture storage mechanism 40 for storing the end-to-end negotiationposture for possible future use between the two modems.

[0069] Dual first-pass negotiation mechanism 34 independently determinesthe maximal data compression capability of each segment, a segment beingdefined as a modem and its associated gateway. End-to-end datacompression capability determination mechanism 36 determines the maximalend-to-end data compression capability based upon such independentlydetermined maximal data compression capability of each segment.Second-pass end-to-end re-negotiation mechanism 38 then establishes thedetermined maximal end-to-end data compression capability for thechannel between the two endpoint modems. Re-negotiation mechanism 38 isso-called because it effectively re-negotiates one or both segments tooptimize the data compression parameters governing the channel, asdescribed above. Those of skill in the art will appreciate that such atwo-pass capability exchange renders data compression and decompressionbetween the modems to be compatible and maximal, thereby greatlyincreasing the efficiency and throughput of the data channel.

[0070] Referring now to FIG. 3, the preferred method of the inventionwill be summarized. At 600, the end-to-end physical layer is terminatedand local physical layer parameters are negotiated at either of segments1 and 3. Such is the function performed by local proxy negotiationmechanism 30 and the other blocks within the modem relay connector ofFIG. 1. At 700 and 800, the dual first-pass negotiations occur forendpoint segments 3 and 1, respectively. Such is the function performedby dual first-pass negotiation mechanism 34 of FIG. 1. At 900, theend-to-end maximum data compression capability of the channel isdetermined. Such is the function performed by end-to-end capabilitydetermination mechanism 36 of FIG. 1. At 1000, the second-passnegotiation of end-to-end compression parameters (e.g. re-negotiation ofthe segment 3 data compression parameters, as described above) occursthat results in maximal and compatible data compression between themodems. Such is the function performed by second-pass, end-to-endre-negotiation mechanism 38 of FIG. 1. It will be appreciated that theresults of the first-pass negotiations for segments 1 and 3 arecommunicated by any suitable means in at least one direction between theendpoint segments, which makes the second-pass negotiation steppossible.

[0071] Finally, those of skill in the art will appreciate that theinvented method and apparatus described and illustrated herein may beimplemented in software, firmware or hardware, or any suitablecombination thereof. Preferably, the method and apparatus areimplemented in software, for purposes of low cost and flexibility. Thus,those of skill in the art will appreciate that the method and apparatusof the invention may be implemented by a computer or microprocessorprocess in which instructions are executed, the instructions beingstored for execution on a computer-readable medium and being executed byany suitable instruction processor. Alternative embodiments arecontemplated, however, and are within the spirit and scope of theinvention.

[0072] Having illustrated and described the principles of our inventionin a preferred embodiment thereof, it should be readily apparent tothose skilled in the art that the invention can be modified inarrangement and detail without departing from such principles. We claimall modifications coming within the spirit and scope of the accompanyingclaims.

We claim:
 1. A two-pass method for achieving maximal data compressionfor a voice frame modem relay channel within a voice frame networkbetween two endpoint modems, wherein each modem is operatively coupledwith an associated gateway thereby defining an endpoint segmentincluding an endpoint modem and its associated gateway, the methodcomprising: first negotiating maximal data compression parameters foreither of the two endpoint segments; communicating such maximal datacompression parameters for at least one of the two endpoint segments tothe other of the two endpoint segments; and second negotiating maximalend-to-end data compression parameters for the modem relay channel basedupon the first negotiated maximal data compression parameters for thetwo endpoint segments.
 2. The method of claim 1 which further comprises:transitioning the channel from a voice mode into a modem relay mode ofoperation.
 3. The method of claim 2, wherein said transitioning includesterminating the end-to-end layer between the two modems and thirdnegotiating at either segment a local physical layer between the twomodems and their associated gateways.
 4. The method of claim 3, whereinsaid third negotiating at one of the endpoint segments of acorresponding physical layer is delayed until said communicating iscompleted.
 5. The method of claim 4, wherein said third negotiating isdelayed by a refusal of the endpoint segment receiving the communicatedmaximal compression parameters to respond to commands from the endpointsegment performing said communicating.
 6. The method of claim 1 whichfurther comprises storing the end-to-end data compression parameters forthe modem relay channel in a memory as an end-to-end negotiationposture.
 7. A method of maximizing data compression between two modemsin a voice frame network wherein each of the two modems is operativelycoupled with an associated gateway defining a segment, the methodcomprising: first negotiating at a first segment the maximum datacompression to determine the maximum data compression capability of thefirst segment and communicating the determined capability from the firstsegment to a second segment; second negotiating at the second segmentthe maximum data compression to determine the maximum data compressioncapability of the second segment; determining the maximum end-to-enddata compression capability of a channel between the two modems;renegotiating at the first segment the determined maximum end-to-enddata compression capability of the channel with respect to the firstsegment.
 8. The method of claim 7 which further comprises: terminatingthe end-to-end layer between the two modems; and negotiating at eithersegment a local physical layer between the two modems and theirassociated gateways, thereby transitioning the channel into a modemrelay mode of operation.
 9. The method of claim 7 which, after saidrenegotiating, further comprises: storing in a memory an end-to-endnegotiation posture of the two modems representative of the maximumend-to-end data compression capability of the channel.
 10. Apparatus formaximizing data compression between two endpoint modems in a voice framenetwork defining a channel therebetween, wherein each of the two modemsis operatively coupled with an associated gateway, with each modem andits associated gateway defining a segment, the apparatus comprising: adual first-pass negotiation mechanism for independently determining themaximal data compression capability of each segment; an end-to-end datacompression capability determination mechanism for determining themaximal end-to-end data compression capability based at least in partupon the independently determined maximal data compression capability ofeach segment; and a second-pass negotiation mechanism for establishingthe determined maximal end-to-end data compression capability for thechannel.
 11. The apparatus of claim 10 which further comprises: anend-to-end negotiation posture storage mechanism for storing in a memorythe determined maximal end-to-end data compression capability for thechannel.
 12. The apparatus of claim 10 which further comprises: a modemrelay connector for transitioning the channel to a modem relay mode ofoperation.
 13. The apparatus of claim 12, wherein said modem relayconnector includes a local proxy negotiation mechanism for terminatingthe end-to-end layer between the two modems and for negotiating ateither segment a local physical layer between the two modems and theirassociated gateways.
 14. A computer-readable medium containing a programfor maximizing data compression between two endpoint modems in a voiceframe network defining a channel therebetween, wherein each of the twomodems is operatively coupled with an associated gateway, with eachmodem and its associated gateway defining a segment, the programcomprising: instructions for first negotiating maximal data compressionparameters for either of the two endpoint segments; instructions forcommunicating such maximal data compressions parameters for at least oneof the two endpoint segments to the other of the two endpoint segments;and instructions for second negotiating maximal end-to-end datacompression parameters for the modem relay channel based upon the firstnegotiated maximal data compression parameters for the two endpointsegments.
 15. The computer-readable medium in accordance with claim 14,which computer-readable medium further comprises: instructions fortransitioning the channel from a voice mode into a modem relay mode ofoperation.
 16. The computer-readable medium in accordance with claim 15,wherein said instructions for transitioning include instructions forterminating the end-to-end layer between the two modems and instructionsfor third negotiating at either segment a local physical layer betweenthe two modems and their associated gateways.
 17. The computer-readablemedium in accordance with claim 16, which computer-readable mediumfurther comprises: instructions for storing the end-to-end datacompression parameters for the modem relay channel in a memory as anend-to-end negotiation posture.
 18. Apparatus for maximizing datacompression between two endpoint modems in a voice frame networkdefining a channel therebetween, wherein each of the two modems isoperatively coupled with an associated gateway, with each modem and itsassociated gateway defining a segment, the apparatus comprising: meansfor first negotiating at a first segment the maximum data compression todetermine the maximum data compression capability of the first segmentand communicating the determined capability from the first segment to asecond segment; means for second negotiating at the second segment themaximum data compression to determine the maximum data compressioncapability of the second segment; means for determining the maximumend-to-end data compression capability of a channel between the twomodems; and means for renegotiating at the first segment the determinedmaximum end-to-end data compression capability of the channel withrespect to the first segment.
 19. The apparatus of claim 18 whichfurther comprises: means for terminating the end-to-end layer betweenthe two modems; and means for negotiating at either segment a localphysical layer between the two modems and their associated gateways,thereby transitioning the channel into a modem relay mode of operation.20. The apparatus of claim 19 which further comprises: means for storingin a memory an end-to-end negotiation posture of the two modemsrepresentative of the maximum end-to-end data compression capability ofthe channel.